U.S. patent number 7,404,383 [Application Number 10/598,128] was granted by the patent office on 2008-07-29 for valve train with cam switching for the gas exchange valves of a four-cycle internal combustion engine.
This patent grant is currently assigned to Schaeffler KG. Invention is credited to Harald Elendt.
United States Patent |
7,404,383 |
Elendt |
July 29, 2008 |
Valve train with cam switching for the gas exchange valves of a
four-cycle internal combustion engine
Abstract
A valve train with cam switching used for intermittent control
of a four-cycle internal combustion engine. The valve train
comprises a splined shaft, one cam block per cylinder, and a
housing-mounted actuator pin. On each end of the cam block is a
cylindrical end piece and a mirror-symmetric displacing groove. A
housing-mounting actuator pin inserts radially into each displacing
groove. The cam block reciprocates axially through the cooperation
of the actuator pins and the displacing grooves when the engine is
running. Low wear of the valve train and a high switching speed are
achieved due to the fact that the displacing grooves possess an
accelerating flank with an impact ramp that results in a constant,
low initial axial speed of the cam block and a feeble impact force
of the actuator pins.
Inventors: |
Elendt; Harald (Altendorf,
DE) |
Assignee: |
Schaeffler KG (Herzogenaurach,
DE)
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Family
ID: |
34832942 |
Appl.
No.: |
10/598,128 |
Filed: |
January 18, 2005 |
PCT
Filed: |
January 18, 2005 |
PCT No.: |
PCT/EP2005/000416 |
371(c)(1),(2),(4) Date: |
August 18, 2006 |
PCT
Pub. No.: |
WO2005/080761 |
PCT
Pub. Date: |
September 01, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070178731 A1 |
Aug 2, 2007 |
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Foreign Application Priority Data
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Feb 21, 2004 [DE] |
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10 2004 008 670 |
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Current U.S.
Class: |
123/90.16;
123/90.6; 123/90.18 |
Current CPC
Class: |
F01L
1/053 (20130101); F01L 13/0036 (20130101); F01L
2820/01 (20130101); F01L 13/0005 (20130101); F01L
1/16 (20130101); F01L 2013/0052 (20130101); F01L
2001/0473 (20130101); F01L 2305/00 (20200501) |
Current International
Class: |
F01L
1/34 (20060101) |
Field of
Search: |
;123/90.15,90.16,90.17,90.18,90.27,90.31,90.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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42 30 877 |
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Apr 1993 |
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DE |
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196 11 641 |
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Jun 1997 |
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DE |
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100 54 623 |
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May 2002 |
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DE |
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101 48 179 |
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Apr 2003 |
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DE |
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101 48 243 |
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Apr 2003 |
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DE |
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0 798 451 |
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Oct 1997 |
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EP |
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Primary Examiner: Chang; Ching
Attorney, Agent or Firm: Lucas & Mercanti, LLP
Claims
The invention claimed is:
1. A valve train comprising cam switching for an intermittent
control of a four-cycle internal combustion engine comprising
following features and components: a splined shaft comprising an
axial outer gearing and one cam block per cylinder, said cam block
comprising an inner gearing through which the cam block can be
axially displaced and connected rotationally fast to the splined
shaft; the cam block comprising per gas exchange valve two cams
arranged adjacent to each other and having identical base circle
diameters and unequal lifts; on each end of the cam block is
arranged a cylindrical end piece, and a mirror-symmetrical
displacing groove is made radially in the periphery of each
cylindrical end piece; a housing-mounted actuator pin for radial
insertion into each displacing groove, the cam block being able to
reciprocate axially through a cooperation of the actuator pins and
the displacing grooves when the engine is running, wherein the
displacing groove possesses an accelerating flank comprising an
impact ramp whose constant, gentle ascending gradient causes a
correspondingly constant, low initial axial speed of the cam block
and a feeble impact force of the actuator pins.
2. A valve train of claim 1, wherein the ascending gradient of the
impact ramp is situated between 5 and 50 .mu.m per degree.
3. A valve train of claim 2, wherein an axial clearance of the
actuator pins in the displacing grooves is 1.2 mm in a run-in
region, decreases to 0.1 mm up to a change-over point between the
accelerating flank and a braking flank, and increases up to a
run-out region to, 0.2 mm.
4. A valve train of claim 3, wherein a base circle region of the
cams extends from a beginning of the impact ramp to an end of a
braking region.
5. A valve train of claim 4, wherein the displacing grooves on the
periphery of the cylindrical end pieces start with a depth run-in
region and end with a depth run-out region and that a depth region
having a constant depth is situated between said depth run-in and
run-out regions.
6. A valve train of claim 5, wherein the depth region begins before
an impact region of the accelerating flank and extends up to the
end of the braking region.
Description
FIELD OF THE INVENTION
The invention concerns a valve train comprising cam switching
typically for an intermittent control of gas exchange valves of a
four-cycle internal combustion engine comprising: a splined shaft
comprising an axial outer gearing and one cam block per cylinder,
said cam block comprising an inner gearing through which the cam
block can be axially displaced and connected rotationally fast to
the splined shaft; the cam block comprising per gas exchange valve
two cams arranged adjacent to each other and having identical base
circle diameters and unequal lifts; on each end of the cam block is
arranged a cylindrical end piece, and a mirror-symmetrical
displacing groove is made radially in the periphery of each
cylindrical end piece; a housing-mounted actuator pin for radial
insertion into each displacing groove, the cam block being able to
reciprocate axially through the cooperation of the actuator pins
and the displacing grooves when the engine is running.
BACKGROUND OF THE INVENTION
Efforts to reduce fuel consumption and pollutant emission in modern
internal combustion engines should obviously also include the
consideration of intermittent or on-off control. With this method,
in which individual cylinders are at least temporarily shut off,
the mean pressure of the still firing cylinders is raised. This
leads to a reduction of the specific fuel consumption. To guarantee
that all the cylinders have the operating temperature required for
an efficient and low-pollution combustion during intermittent
operation, a frequent change-over is necessary between fired and
non-fired cylinders.
DE 101 48 179 A1 discloses a valve lift or cam switching
arrangement that is suitable for an on-off control of the gas
exchange valves of a four-cycle internal combustion engine. This
arrangement has the following features and components: a splined
shaft comprising an axial outer gearing and one cam block per
cylinder comprising an inner gearing through which the cam block
can be axially displaced and connected rotationally fast to the
splined shaft; the cam block comprising per gas exchange valve two
cams arranged adjacent to each other and having identical base
circle diameters and unequal lifts; on each end of the cam block is
arranged a cylindrical end piece, and a mirror-symmetrical
displacing groove is made radially in the periphery of each
cylindrical end piece; a housing-mounted actuator pin for radial
insertion into each displacing groove, the cam block being able to
reciprocate axially through the cooperation of the actuator pins
and the displacing grooves when the engine is running.
For implementing an on-off control, one full lift cam and one zero
lift cam has to be provided for each valve, and these cams are
pushed to and fro during change-over between firing and non-firing
operation. An intrinsic danger arising from the frequent and rapid
switching of the cams is the overloading and wear of the switching
mechanism, particularly of the displacing grooves and actuator
pins.
Comparable, even if moderated, loading conditions for the
displacing grooves and actuator pins are given if the
switching-over of the inlet cams of the cam pairs of the cam block
serves to realize a two-point camshaft adjuster. To this end, the
inlet cams of a cam pair have equal cam lifts but different phases
for the range of low and high engine speeds.
In a similar manner, it is possible to conceive a valve train with
a fully variable mechanical valve lift adjustment in combination
with a cam switching system in which each pair of inlet cams of the
cam block comprises one inlet cam that is optimized for low load
and speed and one inlet cam that is optimized for high load and
speed. In this way, the range of low load and speed can be operated
for favorable consumption and the range of high load and speed can
be operated for high performance. In both these modes of cam
switching, the frequency of switching is low compared to that
required in intermittent control.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a valve train of a
generic type that distinguishes itself by controllable loading and
low wear as also by a high switching speed.
This and other objects and advantages of the invention will become
obvious from the following detailed description.
SUMMARY OF THE INVENTION
The invention achieves the above objects by the fact that the
displacing grooves possess an accelerating flank comprising an
impact ramp whose constant, gentle ascending gradient causes a
correspondingly constant, low initial axial speed of the cam block
and a feeble impact force of the actuator pins. Through these
features, wear of the displacing grooves and actuator pins is
avoided for the most part. This enables a high switching speed and
a minimization of switching noise.
For avoiding wear and overloading of the impact ramps and actuator
pins, it has proved to be advantageous to configure the ascending
gradient of the impact ramp in the range of 5 to 50 .mu.m per
degree.
Advantageously also, the axial clearance of the actuator pins in
the displacing grooves, depending on the tolerances, is, for
instance, 1.2 mm in the run-in region, decreases to, for instance,
0.1 mm up to the change-over point between the accelerating flank
and a braking flank, and increases up to the run-out region to, for
instance, 0.2 mm.
The relatively large axial clearance in the run-in region of the
displacing grooves serves to accommodate positional axial
tolerances of the cylinder head-mounted actuator pins and the
camshaft-mounted displacing grooves.
The small axial clearance between the actuator pins and displacing
grooves in the region of the change-over point results in an almost
jerk-free contact transition of the actuator pins from the
accelerating flank to the braking flank of the displacing grooves.
The somewhat larger axial clearance in the run-out region that is
free from side forces permits a somewhat coarser finishing of this
part of the displacing grooves.
Because the base circle region of the cams extends from the
beginning of the impact ramp to the end of the braking region i.e.,
because it extends in the region of the axial displacing movement
of the cam blocks, a step-less transition from cam to cam is
possible.
Another advantageous feature is that the displacing grooves on the
periphery of the cylindrical end pieces start with a depth run-in
region and end with a depth run-out region and that a depth region
having a constant depth is situated between these depth run-in and
run-out regions.
It is of advantage for the durability of the actuator pins if the
depth region begins before the impact region of the accelerating
flank and extends up to the end of the braking region. During its
loading by the axial displacing force, the actuator pin is thus
situated in the depth region of the displacing groove and is loaded
over its entire length.
In this way, when loaded by side forces, the actuator pins are
situated in the depth region of the displacing grooves, so that the
largest possible surface of the actuator pins and displacing
grooves is available for supporting the side forces.
Further features of the invention result from the following
description and drawings that show a schematic representation of an
example of embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a valve train comprising cam switching for
an on-off control;
FIG. 2 shows a cylindrical end piece comprising a displacing groove
of the invention;
FIG. 3 is a developed view of an accelerating and a braking flank
of the displacing groove of FIG. 2, in a top view and in a
longitudinal section.
DETAILED DESCRIPTION OF THE DRAWINGS
The present invention concerns a four-cycle spark ignition internal
combustion engine comprising a valve train with cam switching. The
valve train comprises a separate inlet and outlet camshaft and two
inlet and outlet valves per cylinder.
FIG. 1 shows a cylinder 1 with parts of this valve train. Among
these are a splined shaft 2, one cam block 3 per cylinder 1, two
actuator pins 4, 5 per cam block 3 and two cam followers 6 with
rollers 7 for two gas exchange valves 8. Theses can serve as inlet
or as outlet valves.
Along its entire length, the splined shaft has an axial outer
gearing 10. Complementary thereto, the cam block 3 comprises an
axial inner gearing through which the cam block 3 is connected
rotationally fast but axially displaceable to the splined
shaft.
On its outer periphery, the cam block 3 comprises a mounting region
11 that serves to support the splined shaft 2. An associated
bearing 12 is arranged in the cylinder 1 centrally between the gas
exchange valves 8.
The mounting region 11 is flanked by partial or zero lift cams 13
and full lift cams 14, that are arranged as cam pairs 15
immediately next to each other and in the same order. The cams 13
and 14 have equal base circle diameters, so that their axial
displacement is possible.
Immediately next to the two cam pairs 15, are arranged cylindrical
end pieces 16, 16a. Each of the cylindrical end pieces 16 and 16a
comprises a displacing groove 17 and 18 respectively, that are
represented schematically in FIG. 1. The displacing grooves 17, 18
have a helical configuration and are mirror-symmetric to each
other, so that each displacing groove 17, 18 has a different
displacing direction. The ends of the displacing grooves 17, 18 run
out into the periphery of the cylindrical end pieces 16, 16a.
The actuator pins 4, 5 are mounted on the cylinder head and can be
moved radially towards the axis of the splined shaft. Through an
alternating introduction of the actuator pins 4, 5 into the
displacing grooves 17, 18 during engine operation, the cams 13, 14
experience an axial displacement corresponding to the width of the
cam. The actuator pins 4, 5 are introduced through a depth run-in
region 9 into the displacing grooves 17, 18 and transported back
through a depth run-out region 9a into their initial position and
locked. The cam block 3 is locked in its respective end
position.
The cams 13, 14 actuate the gas exchange valves 8 through rollers 7
of the cam followers 6. These cam followers 6 are configured as
finger or oscillating levers, but it is also conceivable to use
rocker arms or cup tappets.
Details of the inventive configuration of the displacing grooves
17, 18 are disclosed in FIGS. 2 and 3.
FIG. 2 shows the cylindrical end piece 16 comprising a displacing
groove 17 configured according to the invention. Clearly
perceptible is a depth region 19 that is situated between the depth
run-in region 9 and the depth run-out region 9a. The lateral
limitation of the displacing groove 17 is provided by an
accelerating flank 20 and a braking flank 21.
FIG. 3 shows developments of a top view of the accelerating and
braking flanks 20, 21 and of a longitudinal section of the
displacing groove 17. These developments are identical in the case
of the displacing groove 18.
The distance between the accelerating flank 20 and the braking
flank 21 is the axial clearance of the actuator pin 4 or 5, not
shown, in the displacing groove 17 or 18 and depends on the angular
position of the cam block 3.
The accelerating flank 20 begins with a run-in region 22 in which
the actuator pin 4 passes through the depth run-in region 9 to
plunge into the displacing groove 17. The run-in region 22 ends in
an impact ramp 23. With an ascending gradient of 5 to 50 .mu.m per
degree, this ramp 23 is configured relatively flat so as to keep
the impact shock and thus also the wear of the actuator pin 4 and
the impact ramp 23 at a low level and the switching speed of the
cam block 3 as high as possible.
Parallel to the run-in region 22 of the accelerating flank 20
extends the free-wheeling region 24 of the braking flank 21 with an
axial clearance of 1.2 mm. This relatively large axial clearance
for the actuator pin 4 assures its reliable plunging into the
displacing groove 17 taking into account the axial positional
tolerances of the cylinder head-mounted actuator pin 4 and the
camshaft-mounted displacing groove 17. These axial positional
tolerances are accommodated in the region of the impact ramp 23.
The axial clearance of he actuator pin 4 decreases in the region of
the linear impact ramp 23 whereas the axial speed of the actuator
pin 4 remains constant in this region.
In the accelerating region 25, the axial speed of the cam block 3
increases till a change-over point 26 is reached. At this point, a
transition of contact takes place from the accelerating flank 20 to
the braking flank 21. Because the axial clearance of the actuator
pin 4 in the free-wheeling region 24 of the braking flank 21
decreases to only 0.1 mm till the change-over point 26 is reached,
contact transition is practically free of jerks.
From there on, the free-wheeling region 27 of the accelerating
flank 20 and the braking region 28 of the braking flank 21 begins.
The latter ends in the run-out region 30. In the run-out region 30,
the axial clearance of the actuator pin 4 again reaches a value of
0.2 mm with which the actuator pin 4 emerges from the displacing
groove 17.
The lower part of FIG. 3 shows a developed view of the displacing
groove 17. The depth run-in region 9 opens into the depth region 19
that has a constant depth and is followed by the depth run-out
region 9a. The plunging of the actuator pin 4 into the displacing
groove 17 takes place in the run-in region 22 of the accelerating
flank 20 and in the free-wheeling region 24 of the braking flank 21
whereas emerging takes place in the free-wheeling region 27 of the
accelerating flank 20 and the free-wheeling region 30 of the
braking flank 21.
The base circle region 31 that is of import for the displacement of
the cams starts at the beginning of the impact ramp 23 and ends
with the end of the braking region 28 of the braking flank 21 i.e.,
at the beginning of the depth run-out region 9a of the displacing
groove 17.
The mode of functioning of the valve train of the invention is as
follows:
In FIG. 1, the partial or zero lift cams 13 are activated. In this
starting position, the gas exchange valves 8 open only slightly or
remain completely closed, so that, in the latter case, the cylinder
1 concerned cannot fire. The cam block 3 is locked in its left-hand
position and both actuator pins 4, 5 are situated outside of the
displacing grooves 17, 18.
In FIG. 1, the direction of rotation of the splined shaft 2, when
viewed from the right, corresponds to the clockwise direction. By
the insertion of the actuator pin 5 into the displacing groove 18
and a rotation of the splined shaft 2 in the angular range from 180
to 3600 camshaft angle of the common base circle region 31, the cam
block 3 is displaced towards the right by one cam width and then
locked. This results in an activation of the full lift cams 14, so
that gas exchange functions and the cylinder 1 can fire.
After the actuator pin 5 has passed through the depth profile of
the displacing groove 18, it exits through the depth run-out region
9a at the end of the rotation of the splined shaft.
By an insertion of the actuator pin 4 into the displacing groove
17, the cam block 3 can be re-displaced towards the left into the
starting position, so that the partial or zero lift cams are again
activated.
Due to the inventive configuration of the displacing grooves 17, 18
with the relatively flat impact ramp 23 of the accelerating flank
20, the actuator pins 4, 5 penetrate gently into the displacing
grooves 17, 18 despite the relatively large axial clearance
existing in the free-wheeling region 24. Owing to the feeble axial
clearance at the change-over point 26, the transition of contact
from the accelerating flank 20 to the braking flank 21 takes place
practically without jerks, so that wear of the displacing grooves
17, 18 and actuator pins 4, 5 is avoided for the most part even at
high switching speeds.
* * * * *